[unreadable] Discrete arterial blood gas measurement (ABG) remains as the "gold standard" used by perfusionists to ascertain the effectiveness of their ability to maintain homeostasis during cardiopulmonary bypass. There are two major problems with this practice; ABG only measure one point in a continuing process and in today's environment of cost reduction, the cost associated with each determination, hence long intervals between measurements. One specific example of a commonly occurring condition where ABG is not reliable follows rewarming of pediatric patients during cardiopulmonary bypass. In this situation ABG appear normal, but in fact as tissues rewarm they frequently "release" accumulated CO2 (formed during periods of hypoperfusion), which can first be measured internally by complex tissue tonometry or by increased CO2 in the oxygenator exhaust gas. This differential condition, where tissue CO2 is higher than arterial CO2 is known as "pCO2 gap". The proposed instrument measures this parameter and gives perfusionists early warning that the level of support maybe inadequate. Ension is proposing to develop a gas measurement system that would measure oxygen and carbon dioxide concentrations in blood oxygenator exhaust gas. This system would mitigate the two concerns expressed above. It would be continuous, logging data at intervals as short as one second, thus giving the perfusionist continuous information regarding the adequacy of perfusion. This device would be relatively low-cost and could obviate the need for frequent blood gas measurement. We propose both in vitro testing in our laboratory and ex vivo evaluation at Children's Hospital in Pittsburgh to develop our hardware and algorithms. Preapplication concept evaluation under clinical conditions has demonstrated that large amounts of carbon dioxide, at levels higher than expected, can be present and can be accurately measured in the blood oxygenator exhaust gas. Anecdotally, patients who do not experience this CO2 gap seem to have smoother and faster recoveries. [unreadable] [unreadable]